It is nowadays an accepted fact that a soft, flexible and stretchable rubber material, which clings to the teat, is physiologically more suitable for the milking process than respective hard rubbers. Such soft rubber materials permit a gentler massage of the teat and they cause less constrictions at the teat base. Furthermore, such rubber materials are less irritating to the tissue because they adapt themselves better to the tissue. This will also have the effect that teat rubbers consisting of such a material can also be used more universally, since they adapt themselves better to the various shapes and sizes of the teats. Finally, such teat rubbers also fulfil a better support stocking function for the teat, since, in view of the fact that they are better adapted to the teat, they provide higher friction at the skin of the teat thus preventing an undesirable ascent of the teat rubber towards the teat base.
Although teat rubbers consisting of such a soft material show a particularly large number of advantages, they have hitherto been unable to gain acceptance in everyday practice due to serious other disadvantages. An essential reason for this is to be seen in the fact that the notch toughness as well as the resistance to tearing of the rubber material in question will decrease in proportion to an increase in the softness and adaptability of the teat rubber produced from such a rubber material. The main problem arising, when such soft rubber materials are used, is that these materials are very sensitive to blows, which may be caused quite frequently in the course of the normally rough milking procedure. A part which is especially endangered in this respect is the holding rim of the teat rubber, which engages the milking cup from above. This holding rim is not primarily endangered by kicks of the cow nor by blows hitting the head of the teat rubber in the longitudinal direction of the milking cup. The actual danger is caused by knocks or blows hitting the milking cup sideways from above. That such blows occur quite frequently is due to the structural design of the milking equipment, which is constructed such that the four heavy milking cups are attached to very flexible milk collecting hoses, which have a length of approx. 18 cm, and are suspended from a collecting unit. Every slightly faster movement of the collecting unit, which may occur when the milking equipment is being removed, or when it falls off, or during transport, may result in a correspondingly fast movement of the milking cup. However, due to the fact that the milking cup is guided by the flexible milk hose on the underside thereof, blows will occur in most cases, said blows hitting the upper side of the cup sideways from above, when there is some obstacle. As far as such obstacles are concerned a large number of them exists, such as gratings with sharp edges, the concrete floor, the milking stand edge or the milking frame. If a milking cup hits such an obstacle at the side, the head of the teat rubber will swerve to the side, whereas the holding rim engaging the milking cup from above will be subjected to the full blow. This will have the effect that the holding rim, which is pretensioned to a certain degree, will break through and that small, often unnoticed holes will be formed, the injury and the subsequent breaking through taking normally place from inside. In view of the fact that a pulsating vacuum exists in the space between the teat rubber and the milking cup during the milking process, it will frequently happen that wrong air will enter this pulsation space through the holes caused by said blows, and this will result in poor pulsation. Moreover, it will often happen that, during the milking cup cleaning process, water is additionally sucked into the pulsation space through the holes caused by the above-mentioned blows, and this will have the effect that the pulsation paths will partially be blocked during the subsequent milking process and that, on the whole, a pulsation malfunction will occur, which will finally entail very serious mastitis problems. However, the teat rubbers are, in practice, removed from the milking cups only at major intervals of time so that the problems arising due to the holes caused by the above-mentioned blows will often not be noticed for a very long time.
Numerous attempts have already been made to find possibilities of preventing a breaking through of the teat rubbers at the edges of the milking cup. One possibility would be the use of a harder rubber material on the whole. This would, however, mean that precisely the advantages provided by the use of a soft teat rubber material would have to be given up. Another possibility would be the provision of a teat rubber holding rim which is designed in the form of a thicker bead so as to reduce the probability of breaking through. However, this solution would show the disadvantage that the milking cup heads would become comparatively bulky, since, in particular in the case of cows with closely spaced teats, these heads must be positioned in a very closely spaced relationship, i.e. the diameter at the head should only be comparatively small. In the case of such a solution, additional difficulties would arise, if some types of automatic washing machines were used; in the case of such automatic washing machines, the milking cup head portions are inserted into washing reception means, which produce a sealing effect on the outer side thereof and which, consequently, have a standardized internal diameter. An additional disadvantage of such a bead would become evident in the production of such teat rubbers, since the cost of materials would be increased and, in particular, since a longer vulcanization period would be required, whereby the total expenses would be increased still further.
Moreover, it has already been attempted to design the holding rim of the teat rubber in such a way that, at the location where the edge of the milking cup is positioned, a recess is provided in the holding rim so that the holding rim extends in this area at a certain distance from the milking cup edge and contacts said milking cup only at the smooth outer surface thereof. The rubber of the holding rim can thus deflect to a certain degree prior to coming into contact with the edge of the milking cup.
Furthermore, EP-B1-0 043 264 already discloses attempts to protect the head of the teat rubber against breaking through by means of a special, hard outer cap. Such protective caps can either be attached to the metal cup sleeve or they are fixedly connected thereto. In addition to their bulkiness, any type of protective cap solution shows the disadvantage that dirt will accumulate between the flexible rubber and the cap and that, in practice, it will hardly be possible to remove said dirt. This will result not only in a hygienically untolerable situation--since the process in question is a food production process--but also in the development of fungi, which will grow under the cap on dirt and moisture and which will gradually penetrate the rubber and destroy it. Hence, all types of protective caps are of no use as far as the solution of the problem of breaking through is concerned.
Similar problems arise in the case of the milking cup known from U.S. Pat. No. 4 651 676, in the case of which the teat rubber is provided with a very low head whose outer lower end has formed thereon an annular lip, which engages the upper edge of the milking cup from above. For protecting the head of the teat rubber, a protective ring or a protective cup, which fully encloses the upper head of the teat rubber, is additionally formed on the milking cup, the upper edge of said protective ring or protective cup projecting additionally beyond the upper end of the teat head.
In accordance with another attempt, damping ribs were formed on the outer side of the holding rim in the longitudinal or also in the transverse direction of the teat rubber. In addition to the fact that the desired resistance to breaking through could not be achieved by means of this ribs either, additional hygienic problems arose, since the corners of such ribs are particularly difficult to clean and proved to be dust traps.
Normally, the teat rubber holding rims are formed such that they are tensioned upon being attached to the milking cup. This tension of the holding rim will, of course, increase the risk of breaking through or tearing of the teat rubber, when said teat rubber is subjected to blows. However, if the tension is reduced--and this would be a possibility of reducing the probability of breaking through--this will entail the essentially greater disadvantage that the teat rubber as a whole will no longer reliably adhere to the milking cup, and this may result in an ingress of water into the milking cup intermediate space during the cleaning process as well as in a rotary displacement of the teat rubber, i.e. in wringing out of the teat, during the milking process. The resultant risk of mastitis would exceed by far the advantage which could be achieved by the use of a soft rubber.
In the case of teat rubbers having a very low head height, it may also happen that the holding rim breaks through, if the milking cup hits an obstacle with the teat rubber head-first or if it hits said obstacle sideways from in front. The probability of breaking through of the holding rim could be reduced in these cases by using a high, long teat rubber head whose path of deflection would be longer and whose ability to deflect would be greater. However, these heads entail the disadvantage that the teat supporting effect is not so good and that in the case of short teats the suction pipe will perhaps only take hold of the tip of the teat. This will also have the effect that the milking cup may more easily fall off the teat.
An additional possibility of reducing the risk of breaking through of the holding rim could be seen in the measure of enlarging the diameter of the teat rubber head. Upon milking cows with closely spaced teats, this, however, would entail the same problems which are also entailed by the use of thicker beads for the holding rim. In such cases, it may especially happen that independent milking out of the individual teats would no longer be possible because the individual heads would influence and impede one another.
The present invention is based on the task of preventing the breaking through of the holding rim of teat rubbers and especially the breaking through of the holding rim of teat rubbers consisting of a soft material.
In accordance with the present invention, this task is solved by the features that a recess is provided in the holding rim portion located opposite the milking cup edge portion facing outwards in the longitudinal direction, and that a ring, which consists of a material different from the material of the teat rubber, is adapted to be inserted into said recess.
This will definitely prevent a breaking through behaviour of the holding rim.
A structural design which proved to be expedient is a design in the case of which the ring has, at its side facing the milking cup edge, a structural shape which is complementary to said milking cup edge. Although this will result in an optimum distribution of forces and in an optimum absorption of the impact effect, it still possible to provide an arrangement in the case of which the ring has a shape deviating from the shape of the edge of the milking cup and in the case of which said ring abuts on the edge of said milking cup only via an additional material or via an element consisting of the material of the teat rubber.
The advantages which can be achieved can be improved still further by providing the feature that, at its side facing away from the milking cup edge, the ring is provided with an area having, in comparison with the radius of curvature of said milking cup edge, a larger radius of curvature.
Independently of the shape of the ring, it will be particularly advantageous to choose for the ring a material, which is hard in comparison with the material of the teat rubber and which is slightly flexible.
A substantial increase in the resistance to breaking through can also be achieved, when the ring consists of a soft material having, in comparison with the notch toughness of the teat rubber material, a higher notch toughness.
In particular in cases in which the ring was formed into the holding rim, good results were achieved, when the ring consisted of spring steel, plastic material, hard rubber or textile material.
Plastic materials which proved to be particularly suitable for producing the ring are polyamide, polyethylene, polypropylene, polyester, polyurethane or polyvinyl chloride.
The greatest improvements were achieved in cases in which a teat rubber consisting of silicone rubber was used. On the basis of this improvement, it is now finally possible to take into account an unlimited use of silicone rubber in practical everyday processes.